Owning for a secondhand bike shop in the 70's - 80's, we came upon this issue often. Alignment of the rear triangle and wheel dish is relatively easy to check, so these tasks are done prior to test riding. Checking fork alignment is more difficult. When a bike pulls, we determine which way it is misaligned by which hand needs to be placed behind the bars to track straight. Assuming the rear triangle alignment is correct and the dish of each wheel is ok, if lightly pushing with the left hand behind the bars keeps the bike straight, then the front wheel is aligned too far right in relation to the frame, and we cold-set the fork to the left. If pushing lightly with the right hand makes the bike track straight, then we would cold-set the fork to the right. Remember, this was back when all frames and forks were steel (except the oddball Teledyne or Graftek) so cold-setting was pretty routine.
Kevin